Zeolites, although generally viewed as having broad compositional substitution possibilities (Pure and Appl. Chem. (1979), 51, p. 1091), are usually defined as crystalline hydrated aluminosilicates of Group I and Group II elements. In particular, those elements include sodium, potassium, calcium, magnesium, barium and strontium. The structure of zeolites is typically an aluminosilicate framework based on an indefinitely extending three dimensional network of Alo.sub.4 and SiO.sub.4 tetrahedra linked to each other by sharing of the corner oxygens. Zeolites are often represented by the empirical formula M.sub.2/n O.cndot.Al.sub.2 O.sub.3 .cndot. x SiO.sub.2 .cndot. y H.sub.2 O. In this oxide formula, x is generally greater or equal to 2 since AlO.sub.4 tetrahedra are joined only to SiO.sub.4 tetrahedra, and n is the Group I or Group II cation valence. The framework contains channels and interconnected voids which may be occupied by the cation and by water molecules. The cations are often quite mobile and may be exchanged by other cations. Intracrystalline zeolitic water may be reversibly removed. In some zeolites, cation exchange or dehydration may produce structural changes in the framework.
Much zeolite research has focused on the synthesis of zeolite frameworks containing elements other than silicon and aluminum. It is known that gallium ions and germanium ions may be substituted for aluminum and silicon cations in the framework. While an extensive family of aluminum-phosphorus zeolites (AlPO's) has recently been synthesized, the substitution of other elements is the subject of major controversy in the zeolite literature. For instance, U.S. Pat. Nos. 3,329,480 and 3,329,481 both issued to D. A. Young, report the existence of crystalline zirconosilicate and titanosilicate zeolites. A zeolite having chromium in the tetrahedral positions has been described by Yermolenko et al at the Second Oil Union Conference on Zeolites, Leningrad, 1964, pages 171-8 (published 1965). However, D. W. Breck, in Zeolite Molecular Sieves, p. 322, John Wiley & Sons (1974) suggests that the chromium present was not present in a zeolite A structure and furthermore was present as an impurity in insoluble form. The impurity was said to be in the form of a chromium silicate as confirmed by the nature of the water vapor adsoption isotherm. This subject has been reviewed by Barter, "Hydrothermal Chemistry of Zeolites", Academic Press (1982), p. 294.
Because of the presence of phosphorus in tetrahedral PO.sub.4 units in certain rare zeolites, extensive work has been done to synthesize zeolites containing PO.sub.4 tetrahedral. Various phosphorus containing zeolites have been prepared and reported in Breck, supra, p. 323 et seq. The synthesis technique for production of phosphorus-containing zeolites generally involves crystallization from a gel in which the phosphorus is first incorporated by a controlled copolymerization and coprecipitation of all of the component oxides in the framework, i.e., aluminate, silicate, and phosphate in the homogeneous gel phase. The crystallization of the gel is then carried out at a temperature between 80.degree. C. and 210.degree. C.
The synthesis of major iron-containing zeolitic structures has been reported. Japanese Kokai 59,121,115, published Jul. 13, 1984, disclosed an aluminosilicate having a faujasite structure and containing coordinated iron. The chemical composition is said to be of the formula aM.sub.2/n O.cndot.b Fe.sub.2 O.sub.3 .cndot.Al.sub.2 O.sub.3 cSiO.sub.2 where M can be H, alkali metal or alkaline earth metal. The symbol n is the valence of M; a=1.+-.0.3; c is between 4.6 and 100; and a is less than b and both are less than 7. The relation between the IR absorption wave number (y) in cm.sup.-1 and the crystal lattice parameter a.sub.o is said to be expressed as Y.ltoreq.-116.7a.sub.o +3920.
Similarly, U.S. Pat. No. 4,208,305 (Eur. Pat. No. 115,031.cndot.A) discloses a crystalline ferrosilicate having the general formula: EQU aM.sub.2/n O.cndot.(Al.sub.x Fe.sub.1-x).sub.z O.sub.3 .cndot.bSiO.sub.z
where M is a cation of valence n, a=0-2.0, b=3-100 and z=0-0.98. The composition is said to have a uniform pore diameter of 4-5.ANG. and a characteristic x-ray powder diffraction pattern of:
______________________________________ 2.THETA. d(.ANG.) Rel. Intensity ______________________________________ 10.9-11.1 8.12-7.97 M-VS 13.4-13.5 6.61-6.56 M-S 17.4-17.5 5.10-5.07 M-S 21.0-21.1 4.23-4.21 M-S 22.0-22.1 4.40-4.02 M-VS 20.6 3.121 M-S 32.3-32.4 2.772-2.763 M-S ______________________________________
The composition is formed by maintaining a mixture having a molar oxide composition of: 0-10 R.sub.2 O:1-15 M.sub.2/n :(Al.sub.x Fe.sub.1-x).sub.2 O.sub.3 : 10-200 SiO.sub.2 :200-1000 H.sub.2 O where R is an organic templating agent.
A range of metallo-alumino-phosphates and metallo-silico-alumino-phosphates compositions have recently been reviewed (Flanigen et al, in "Innovations in Zeolite Materials Science", Ed. Grobet et al, SSSC v. 37, p. 13 (Elsevier)). The structure and composition of the present invention has not been reported in such families of materials.
None of this literature discloses a transition-metal-alumino-silicate composition having a mazzite-like structure and having the chemical composition disclosed herein, and its use as a hydrocarbon conversion catalyst.